In recent years, rechargeable electric storage devices such as battery cells (such as lithium ion battery cells and nickel hydrogen battery cells) and capacitors (such as electric double layer capacitors) have been employed as power sources, for example, for vehicles (such as automobiles and motorcycles) and various equipment (such as mobile terminals and laptop computers). For example, a battery cell includes an electrode assembly and a case. The case includes a case body housing the electrode assembly and a cover plate configured to close an opening of the case body. A current collector is connected to the electrode assembly. The electrode assembly and the current collector are arranged inside the case. An external terminal is, for example, arranged on the outer surface of the cover plate. The external terminal and the current collector are connected directly or indirectly to each other. Thus, the external terminal and the electrode assembly are electrically connected to each other.
As a method for electrically connecting the external terminal and the current collector to each other, a conductive member is used. The conductive member includes a first conductive member and a second conductive member. The first conductive member includes a body part, a first swaged part projecting from the lower surface of the body part and a second swaged part projecting from the upper surface of the body part. The second conductive member has two through holes. The second swaged part of the first conductive member and a shaft of the external terminal are respectively inserted through the two through holes.
In a battery cell disclosed in Patent Literature 1, a first conductive member (auxiliary terminal 8) includes a body part (base part 8a), a first swaged part (first swaged tube 8b), and a second swaged part (second swaged tube 8c). An external terminal (external terminal 4) includes a head (base part 4a) and an externally threaded part (bolt part 4b). A second conductive member (connection conductor 9) includes two through holes (a swaging hole 9a and a terminal through-hole 9b). The first conductive member is arranged on the outer surface of a cover plate (cover plate 3) via a sealing member (external insulation sealing member 6). The first swaged part of the first conductive member is inserted through a through hole of a current collector (current collecting connector 5) inside the case. The tip portion of the first swaged part projecting downwardly through the through hole is swaged from below. Further, the external terminal is arranged on the outer surface of the cover plate via a terminal detent member that is provided in the sealing member or separately from the sealing member. The second swaged part of the second conductive member and the externally threaded part of the external terminal are respectively inserted through the two through holes of the second conductive member. The tip portion of the second swaged part projecting upwardly from one of the through holes (the swaging hole 9a) is swaged from above. This allows the external terminal and the current collector to be electrically connected to each other via the first conductive member and the second conductive member.
In the battery cell disclosed in Patent Literature 1, the second swaged part of the first conductive member is swaged to the second conductive member. Therefore, the second conductive member is connected to the first conductive member. The second swaged part prevents space saving on the upper surface of the second conductive member.
Therefore, the second conductive member is welded to the first conductive member, thereby omitting the second swaged part from the first conductive member. It is conceivable that space saving on the upper surface of the second conductive member is thus achieved. However, there are cases where the first conductive member and the second conductive member are produced using different metals. In such a case, the first conductive member and the second conductive member are connected to each other by welding the different kinds of metals. Generally, welding of different kinds of metals is not preferable because a welding failure tends to occur.
Welding the first conductive member and the second conductive member for space saving on the upper surface of the second conductive member is also required in the same manner as in battery cells of a welding type in which a bus bar is welded to a second conductive member serving as an external terminal.
Further, this type of problem is not limited to battery cells. This type of problem also applies to capacitors (such as electric double layer capacitors) as well.